The present invention relates to lighting systems and more particularly to a luminaire for illuminating a task supported on a horizontal work surface.
Heretofore, a wide variety of lighting systems have been proposed for general office and home use. Certain of these systems have been designed to illuminate tasks which are positioned on a horizontal work surface such as a desk. Such task lighting systems may be mounted over the work area and/or suspended from shelves, bookcases and the like. Depending upon the particular type of task being viewed, the light source may be reflected off the task and seen by the observer. Reflection of the light source is directly related to the specularity of the task. For example, when the observer is reading or viewing a shiny magazine page, the light source may be seen and glare or "veiling reflections" occur. Task lighting systems or luminaires, while being designed to provide a predetermined or required illumination at the area of the task, should also be designed to control the specular brightness of the task to avoid such veiling reflections.
Veiling reflections may be a problem only with certain types of tasks. For example, if a light, diffuse paper, such as bond paper, is the task and the user is employing a black felt tip pen, veiling reflections are not a problem.
Various proposals have been made to eliminate or control veiling reflections. Typical prior approaches have reduced the brightness of the light source at the central area thereof. These approaches in effect "place" the light source out of a defined zone within which the task is expected to be positioned. An example of one such system employs a lens which has a so-called "bat-wing" light distribution pattern. The lens system in effect redirects light to the sides of the work surface and reduces the energy or brightness levels in defined directions in which any task specularly will reflect it to the viewer.
Another approach which has heretofore been employed is to place a baffle such as an opaque plate at the central area of the light source. The baffle prevents transmission of light from an area of the light source to the task. The task is illuminated by side lighting. Veiling reflections are eliminated as long as the task is positioned in a defined zone. Should the user move the task to the sides of the work surface, veiling reflections will again become a problem with either the "bat-wing" lens or the baffle approach.
The aforementioned prior approaches to eliminating veiling reflections have merely "blocked" the central area of the source and permitted side light to illuminate the task sufficiently for viewing and/or reading purposes.
An example of one prior system may be found in U.S. Pat. No. 4,054,793, entitled LIGHTING SYSTEM and issued on Oct. 18, 1977, to Shemitz. This patent discloses a lighting fixture including an elongated housing, a light source and a refractor element which distributes luminous flux from the light source in a bat-wing configuration. Another example of a refractor plate which distributes luminous flux from the light source in a bat-wing configuration may be found in U.S. Pat. No. 3,258,590, entitled PLATES FOR LIGHT CONTROL and issued on June 28, 1966, to Goodbar.
Other task lighting systems have attempted to control veiling reflections by polarizing the light emanating from the light source before it strikes the task. When a polarizing filter material is placed in front of the light source so that it is intercepted by light emanating towards the task, the light is polarized before it strikes the surface. This polarization, of course, eliminates one of the components of the light. Upon reflection, the remaining component is also eliminated. This polarizing concept does not block light emanating from the light source. An example of a polarizing system may be found in U.S. Pat. No. 3,239,659, entitled GLARE-REDUCING LAMP and issued on Mar. 8, 1966, to Makas.
In situations where veiling reflections are not a problem because of the task characteristics, the brightness level of the luminaire could desirably be increased. This would increase the illumination which may be wanted by the user. Prior systems have not provided for ready adjustability of illumination levels.
A need exists for a luminaire or task lighting system which will control veiling reflections across the entire work surface yet which permits adjustment of illumination levels to the particular task being viewed and which accommodates differences in geometric orientation, task position, observer eye position and the height of the luminaire above the task so that the user can maximize the effectiveness of the luminaire.